The immediate inspection of tunnels has been ordered across Japan after nine people were killed when concrete ceiling slabs fell from the roof of a highway tunnel onto moving vehicles below.

Those killed in Sunday's accident were traveling in three vehicles in the 4.7-kilometre long Sasago Tunnel about 80 kilometres west of Tokyo. The tunnel, on a highway that links the capital to central Japan, opened in 1977 and is one of many in the mountainous country.

The transport ministry ordered that inspections be carried out immediately on 49 other tunnels around the country that are either on highways or roads managed by the central government and of similar construction.

Police and the highway operator Central Japan Expressway Co. were investigating why the concrete slabs in the Sasago Tunnel collapsed. An inspection of the tunnel's roof in September found nothing amiss, according to Satoshi Noguchi, a company official.

An estimated 270 concrete slabs, each weighing 1.4 metric tons, suspended from the arched roof of the tunnel fell over a stretch of about 110 metres, Noguchi said.

The operator was exploring the possibility that bolts holding a metal piece suspending the panels above the road had become aged, he said. The panels, measuring about 5m by 1.2m, and 8 centimetres thick, were installed when the tunnel was constructed in 1977.

Company President and CEO Takekazu Kaneko said that the company was inspecting other tunnels of similar structure, including a parallel tunnel for traffic going in the opposite direction. Both sections of the highway were shut down indefinitely.

Recovery work at the tunnel was suspended overnight (NZ time) while the roof was being reinforced to prevent more collapses, said Jun Goto, an official at the Fire and Disaster Management Agency

Yoshihiro Seto, an officer with the Yamanashi prefectural police, said they can't rule out that there are more bodies or survivors in the tunnel, but the possibility is low. Goto said they hope to resume recovery work later today (NZ time).